Electrical apparatus and method of making same



Aug. 29, 1961 R. c. MATTER ET AL 2,997,776

ELECTRICAL APPARATUS AND METHOD OF MAKING SAME Filed May 26, 1958INVENTOR5 ROBERT C. MATTER JA M55 R. 5!!15 BY i\ M 7115/ ATTOH N [YInited States This invention relates to insulated cores for electricalapparatus and is particularly concerned with insulated cores having acoextensive insulating coating thereover including an epoxy resin.

One of the objects of the invention is to provide an electrical core oflaminated structure which has a coextensive insulating coating thereoveras applied by suspending a heated core in a fluidized coating materialwhereupon the coating is uniformly disposed in a coextensive layer onthe core.

In carrying out this object, it is a further object to utilize afluidized bed of epoxy containing materials in conjunction with mica inpredetermined quantities to aid in toughening the coating and improvingthe adhesion thereof.

A still further object of the invention is to provide a method forcoating laminated articles with an epoxy containing particles includingmica wherein a fluidized bed of particles of the coating material areused as a means for depositing the particles on a heated and suspendedarticle to be coated.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had to the accompanyingdrawings wherein preferred embodiments of the present invention areclearly shown.

In the drawings:

FIGURE 1 is a view, in perspective, of a laminated electrical core withwindings thereon wherein a portion is broken away to show the coating.

FIGURE 2 is an enlarged fragmentary sectional View of a corner of thecore shown in FIGURE 1 with a portion of the coating broken away.

In electrical apparatus, laminated cores are frequently used to improvethe electrical characteristics of the unit and these cores arefrequently wound with conductors having very thin insulating coatingsthereover. The insulation on these conductors frequently cuts away dueto vibration and tension at the edges of the core to short out theconductors and reduce or destroy the electrical characteristics of theapparatus. Laminated cores are generally made from a plurality ofstamped sheets of soft iron and these stampings have sharp edges thatreadily bite into thin insulating layers. In order to obviate thesedifficulties, it has been past practice to utilize heavy insulatinglayers on or between conductors wound onto laminated cores. These heavyinsulating layers are not only expensive to produce but also tend tospace the conductor farther away from the core and thereby reduce theelectrical efiiciency of the magnetic circuit.

The present invention is directed to a laminated electrical core for usein electrical apparatus wherein the core is provided with a coextensiveand very thin coating of a tough and strong insulating material whereinbare conductors may be wound thereover so long as the turns are spacedfrom one another or wherein very thinly insulated conductors may bewound thereover with out the danger of the insulation being cut throughor failing. This provision increases the efiiciency of the core andreduces the over-all cost of the apparatus in which the core isutilized.

It is understood that this invention may be used with equal facility inany number of electrical applications atent 2,997,776. Patented Aug. 29,1961 2 such as on relay cores, transformer cores, dynarnoelectricmachine armatures and stators and, in fact, in any application wherein alaminated core which requires a winding thereon is to be used, or, infact, on any metal object that requires a tough, relatively thin wearand tear resistant insulating coating.

Referring specifically to the drawings, FIGURE 1 shows a laminated coreat 20 fabricated from a plurality of separate plates of soft iron 22each of similar cross section stacked together and held in place bymeans of a plurality of rivets 24 passing through the plates. Over thecore 20 is disposed a coextensive covering of an insulating material 26to be described in detail hereinafter. Over this insulating material iswound a pair of conductors 28 and 30 on opposed legs of the core. Inthis instance, the core may be a transformer core and the conductor 28may be the primary winding while the conductor 30 may be the secondarywinding. The conductors may be bare wire or ribbon or, if a heavierwinding is desired, may be lightly insulated wire such as varnished wireor equivalent where the turns are wound one upon another wherein severallayers are present, it being understood that any type of winding wellknown in the art may be used.

Referring to FIGURE 2, an enlarged fragmentary corher of the core 20 isshown wherein the laminations 22 are enlarged and wherein thecoextensive insulating covering 26 is shown in more detail. It will beseen that this covering 26 covers all edges of the core with a tough,firmly adhered layer that prevents the wire from cutting into the layerand shorting out on the sharp edges of the laminations of the core.

Specifically, this coating material is, in the preferred embodiment, asolid phase epoxy resin fortified with mica in order to provide thenecessary toughness to the film. The specific application of the filmand the means for incorporating the mica therein are both of utmostimportance to the success of the invention.

To set forth the procedure involved in compounding a material for thecoating process, the following examples are set forth.

Example I The coating composition in this instance comprises:

Parts by weight Epoxy resin 70 325 mesh mica 30 Dicyanodiamide hardener9 Example II The coating mixture in this instance comprises:

Parts by weight Epoxy resin 325 mesh mica 20 Dicyanodiamide hardener 9Here again, the epoxy resin is melted and the mica is dispersedtherethrough after which the mixture is permitted to harden and isground so that all of the mixture will pass a 60 mesh screen, preferably60-200 mesh. The hardener is blended through the powder mixture and thematerial is ready for use.

In each of Examples I and II, it may be desirable to ball-mill theepoxy-coated particles of mica for several hours prior to theincorporation of the hardener therein.

This densifies the particles and improves the mixture.

Ball-milling may be carried out in a standard ball mill with #3 granitechips with the mill rotating at 30 r.p.m.

As an alternative method for coating the mica, the melting and grindingoperations may be eliminated and the mica may be coated entirely byball-milling together the mica and epoxy resins. The same conditionspreviously noted for ball-milling should be used and the mill should berun for about seven and one-half hours or until such time as the coatingis complete.

In Examples I and II, the epoxy resin is preferably a solid phase resinhaving an equivalent weight of about 175, or stated differently, theresin has an epoxide equivalent of about 900. The equivalent weight inthis instance is the number of grams of epoxy resin which will esterifycompletely one gram molecular weight of a monobasic acid. The epoxideequivalent may be defined as the grams of resin containing one gramequivalent Weight of epoxide. It is understood that other epoxy resinshaving varying equivalent weights, for example, of about 150 to 210, maybe used (or. epoxide equivalents of about 500 to 3500), but, in eachinstance, the resin must be a solid in order to perform the mixingfunction with the mica. The hardener may be any suitable amine typehardener or may be one of the formaldehyde resins, for example, uncuredphenol formaldehyde, urea formaldehyde or melamine formaldehyde resin.These are all well known curing or hardening agents for epoxy resins andthey may be used as the entire curing agent or as a portion of thecuring agent, as desired. It is to be understood that, as the equivalentweight or epoxide equivalent of the epoxy resin varies, the hardener ispreferably also varied to cause the reaction to occur within a giventime period and these variations are well known in the art. The epoxyresins in all cases are well known commercial resins generally formed byreaction between bisphenyl A and epichlorohydrin.

The coating operation may be performed by placing a suitable quantity ofthe mica fortified epoxy mixed with the hardener in a compartment ortank wherein a fluid vehicle such as air or other nonreactive gaseousfluid is blown through a bed of the particles causing the particles tobecome fluid-like in nature and to be suspended in a turbulent cloud orlayer wherein the powder is maintained suspended by means of theascending flow of fluid. The electrical part or core to be coated isheated to a temperature of preferably about 400 F. (above the meltingpoint of the epoxy resin used) and is suspended in thisfluidizedresinous material. "Particles of the resinous material whichimpinge on the hot core are at least superficially melted at theirpoints of contact with the core and are adhered thereto whereby theentire core is coated uniformly with the powder. The period of timethrough which the fluidizing process is carried out determines, to alarge degree, the thickness of the coating to be deposited. After thecore is removed from the fluidizing chamber, it is preferably heated toa temperature in the order of 400 F. for about one hour to fully curethe coating and to densify the same. We prefer to utilize coatings inthe order of from .018 to .020 inch thick although coatings from .015 to.025 are generally satisfactory for the purpose of insulating the core.It is understood that these figures may vary by choice for diiferentapplications. Apparatus for applying fluidized coatings from 'solidpowdered material are well known and are readily purchased on themarket.

The mica'is an important addition as it is this ingredient whichimproves edge strength and toughness of the film. It has been found thatsimilar epoxy films placed on cores Without the mica therein do not havethe edge strength nor the coverage and are not as rugged as filmsincluding the mica. Furthermore, the mica acts as a filler and reducesthe cost of the coating whileimprovingits physical characteristics. .Inall cases, the mica must be coated with the epoxy or no satisfactorycoating can be formed.

When following the procedures noted herein, the hardener is preferablynot added to the epoxy-mica mixture until the time it is to be fluidizedwhereby no chemical reaction is initiated until such time that thefluidized particles impinge upon the hot core at which instant at leasta partial chemical reaction occurs which is caused to go to completionby the subsequent curing of the core.

The use of the fluidizing bed as a means for depositing the coating onthe core is very important since, while spraying of particles onto thecore, dipping the core in a varnish, or other means of applying thecoating to the core can be used, the fluidizing process provides moreuniform films than are possible by other methods whereby the efiiciencyof the electrical apparatus is improved and the cost of the coating isreduced. Furthermore, fluidizing makes possible a film of controlledthickness wherein the thickness is easily controlled by the period ofimmersion in the fluidized bed. Fluidizing apparatus for accomplishingthe desired results is well known in the art and is extensively used.

A specific application of the present invention is disclosed incopending application S.N. 737,801, filed concurrently herewith andassigned to the assignee of the present invention.

While the embodiments of the present invention as herein disclosedconstitute preferred forms, it is to be understood that other formsmight be adopted.

What is claimed is as follows:

1. In a method for applying a coextensive insulating coating having anepoxy resin base including a mica filler therein onto the surface of anelectrical core, the steps of; mixing the mica and epoxy resin bymelting the epoxy resin and incorporating the mica therein, grinding thesolidified epoxy resin with the mica therein to a suitable mesh size toform a filled epoxy powder, mixing the filled epoxy powder with asuitable hardener in suflicient quantities to subsequently harden thefilled epoxy powder, and then suspending a hot core to be coated in afluidized bed of said filled resin powder wherein the core is heated toa temperature suflicient to cause at least partial melting of filledepoxy particles that impinge thereon, maintaining the heated core in thefluidized bed of filled epoxy particles for a time sufiicient to obtaina coextensive coating of the desired thickness and then removing thecoated core from the fluidized bed and consolidating the coating thereonby further heating at a temperature suflicient to complete the chemicalreaction of the hardener on the epoxy resin whereby an insulated core isobtained having a coextensivecoating of a tough and wear-resistant epoxyresin thereover and thereafter winding a coil of wire onto the core.

2. 'In a method for applying a coextensive insulating coating having anepoxy resin base including a mica filler therein onto the surface of anelectrical core, the steps of; mixing the mica and epoxy resin bymelting the epoxy resin and incorporating the mica therein, grinding thesolidified epoxy resin with the mica therein to a suitable mesh size toform a filled epoxy powder, mixing the filled epoxy powder with asuitable hardener in sufiicient quantities to subsequently harden thefilled epoxy powder, and then suspending 'a hot core to be coated in afluidized bed of said filled resin powder wherein the core is heated toa temperature suflicient to cause at least partial melting of filledepoxy particles that impinge thereon, maintaining the heated core in thefluidized bed of filled epoxy particles for a time sufiicient to obtaina coextensive coattherein onto the surface of an electrical core, thesteps of; mixing the mica and epoxy resin in a ratio of 20 to 30 partsmica to 70 to 80 parts resin by Weight, grinding the solidified epoxyresin with the mica therein to a suitable mesh size to form a filledepoxy powder, mixing the filled epoxy powder with a suitable hardener ofsuitable mesh size and in suflicient quantities to subsequently hardenthe filled epoxy powder, and then suspending a hot core to be coated ina fluidized bed of said filled resin powder wherein the core is heatedto a temperature suflicient to cause at least partial melting of filledepoxy particles that impinge thereon, maintaining the heated core in thefluidized bed of filled epoxy particles for a time sulficient to obtaina coextensive coating having a thickness in the order of .015 to .025inch thereon and then removing the coated core from the fluidized bedwhereby an insulated core is obtained having a coextensive coating of atough and wear-resistant epoxy resin thereover and thereafter winding acoil of wire onto the core.

4. In a method for applying a coextensive insulating coating having anepoxy resin base including a mica filler therein onto the surface of anelectrical core, the steps of; mixing the mica and epoxy resin bymelting the epoxy resin and incorporating the mica therein, grinding thesolidified epoxy resin with the mica therein to at least 60 mesh size toform a filled epoxy powder, mixing the filled epoxy powder with asuitable hardener having a mesh size of at least 60 and in suflicientquantities to subsequently harden the filled epoxy powder, and thensuspending a hot core to be coated in a fluidized bed of said filledresin powder wherein the core is heated to a temperature suflicient tocause at least partial melting of filled epoxy particles that impingethereon, maintaining the heated core in the fluidized bed of filledepoxy particles for a time suflicient to obtain a coextensive coatinghaving a thickness in the order of .015 to .025 inch thereon and thenremoving the coated core from the fluidized bed and consolidating thecoating thereon by further heat- 6 ing at a temperature sufiicient tocomplete the chemical reaction of the hardener on the epoxy resinwhereby an insulated core is obtained having a coextensive coating of atough and wear-resistant epoxy resin thereover and thereafter winding acoil of wire onto the core.

5. In a method for applying a coextensive insulating coating having anepoxy resin base including a mica filler therein onto the surface of ametal object, the steps of; intimately mixing the mica and epoxy resinfor incorporating the mica therein, grinding the solidified epoxy resinwith the mica therein to at least mesh size to form a filled epoxypowder, mixing the filled epoxy powder with a suitable hardener having amesh size of at least 60 and in sufficient quantities to subsequentlyharden the filled epoxy powder, and then suspending a hot metal objectto be coated in a fluidized bed of said filled resin powder wherein theobject is heated to a temperature suflicient to cause at least partialmelting of filled epoxy particles that impinge thereon, maintaining theheated object in the fluidized bed or" filled epoxy particles for a timesufficient to obtain a coextensive coating having a thickness in theorder of .015 to .025 inch thereon and then removing the coated objectfrom the fluidized bed and consolidating the coating thereon by furtherheating at a temperature sufiicent to complete the chemical reaction ofthe hardener on the epoxy resin whereby an insulated object is obtainedhaving a coextensive coating of a tough and wear-resistant epoxy resinthereover and thereafter winding a coil of wire onto the core.

References Cited in the file of this patent UNITED STATES PATENTS2,469,100 Andrus May 3, 1949 2,561,982 Hanna et al. July 24, 19512,594,096 Trigg Apr. 22, 1952 2,662,070 Kass Dec. 8, 1953 2,780,787Somerville Feb. 5, 1957 2,785,383 Foster Mar. 12, 1957

